The role of temperature in enhancing the insecticidal activity of Bacillus thuringiensis against Spodoptera littoralis larvae

The present study scrutinised how far temperature would affect the velocity of the insecticidal activity of Bacillus thuringiensis, as the rapidity of pest control achievements is of a great concern. Third instar Spodoptera littoralis larvae were treated with Bt at three concentration levels under five different temperatures (15°C, 20°C, 25°C, 30°C and 35°C). LT₅₀s were evaluated in each case. The LT₅₀ values showed various levels of reductions as temperature and/or Bt concentration increased, indicating that the velocity of mortality (1/LT₅₀) and/or the rapidity of Bt activity was almost temperature dependant. However, relatively high and low reduction percentages in the LT₅₀ values on the elevation of 5°C were obtained at lower and higher temperature ranges, respectively. The temperature coefficient, Q ₁₀ values, determined within narrow ranges (5°C) showed great reductions when temperature increased from 15°C to 20°C at all Bt concentrations. Raising temperature by 5°C above 20°C or 25°C almost caused similar Q ₁₀ values indicating constant increase in the response of Bt activity within 20–30°C temperature range. Q ₁₀ values over 30°C were comparatively very low. This proved that decrease in Q ₁₀ values due to the rise of temperature was dependant on the starting temperature.     

Effects of acute temperature change on the metabolism and swimming ability of juvenile sterlet sturgeon (Acipenser ruthenus,Linnaeus 1758)

The objective of this study was to provide information on changes in the metabolism and swimming ability of juvenile sterlet sturgeon, Acipenser ruthenus, caused by acutely low or high temperatures. Changes in critical swimming speed (U_crit), oxygen consumption rate (MO₂), tail beat frequency (TBF) and tail beat amplitude (TBA) were observed with a Steffensen‐type swimming respirometer, an oxygen electrode and a camera at different swimming speeds at three temperatures: 5°C, 15°C, and 25°C. Fish tested at 5°C and 25°C were maintained at 15°C (near optimal) for one week to simulate conditions below a dam. The U_crit value decreased significantly during acute temperature changes at 5°C and 25°C; U_crit was highest near the optimal temperature. Oxygen consumption rate (MO₂) increased with the swimming speed at 15°C; however, at 25°C and 5°C, the MO₂ decreased with the swimming speed. Both TBA and TBF decreased at 5°C and 25°C compared to values at 15°C. The slopes of the regression lines (TBF/U) at 5°C and 25°C seemed lower compared to 15°C.     

Growth at moderately elevated temperature alters the physiological response of the photosynthetic apparatus to heat stress in pea (Pisum sativum L.) leaves

The impact of heat stress on the functioning of the photosynthetic apparatus was examined in pea (Pisum sativum L.) plants grown at control (25 °C; 25 °C-plants) or moderately elevated temperature (35 °C; 35 °C-plants). In both types of plants net photosynthesis (P_n) decreased with increasing leaf temperature (LT) and was more than 80% reduced at 45 °C as compared to 25 °C. In the 25 °C-plants, LTs higher than 40 °C could result in a complete suppression of P_n. Short-term acclimation to heat stress did not alter the temperature response of P_n. Chlorophyll a fluorescence measurements revealed that photosynthetic electron transport (PET) started to decrease when LT increased above 35 °C and that growth at 35 °C improved the thermal stability of the thylakoid membranes. In the 25 °C-plants, but not in the 35 °C-plants, the maximum quantum yield of the photosystem II primary photochemistry, as judged by measuring the F_v/F_m ratio, decreased significantly at LTs higher than 38 °C. A post-illumination heat-induced reduction of the plastoquinone pool was observed in the 25 °C-plants, but not in the 35 °C-plants. Inhibition of P_n by heat stress correlated with a reduction of the activation state of ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco). Western-blot analysis of Rubisco activase showed that heat stress resulted in a redistribution of activase polypeptides from the soluble to the insoluble fraction of extracts. Heat-dependent inhibition of P_n and PET could be reduced by increasing the intercellular CO₂ concentration, but much more effectively so in the 35 °C-plants than in the 25 °C-plants. The 35 °C-plants recovered more efficiently from heat-dependent inhibition of P_n than the 25 °C-plants. The results show that growth at moderately high temperature hardly diminished inhibition of P_n by heat stress that originated from a reversible heat-dependent reduction of the Rubisco activation state. However, by improving the thermal stability of the thylakoid membranes it allowed the photosynthetic apparatus to preserve its functional potential at high LTs, thus minimizing the after-effects of heat stress.     

Biomechanical comparison of implant inclinations and load times with the all-on-4 treatment concept: a three-dimensional finite element analysis

The purpose of this study was to compare the effects of implant inclinations and load times on stress distributions in the peri-implant bone based on immediate- and delayed-loading models. Four 3D FEA models with different inclination angle of the posterior implants (0°, 15°, 30°, 45°) were constructed. A static load of 150?N in the multivectoral direction was applied unilaterally to the cantilever region. The stress distributions in the peri-implant bone were evaluated before and after osseointegration. The principal tensile stress (σ_max), mean principal tensile stress (σ_max), principal compressive stress (σ_min) and mean principal compressive stress (σ_min) of the bone and micromotion at the contact interface between the bone and implants were calculated. In all the models, peak principal stresses occurred in the bone surrounding the left tilted implant. The highest σ_max and σ_min were all observed in the 0° model for both immediate- and delayed-loading models. And the 0° and 15° models showed higher σ_max and σ_min values. The 0°models showed the largest micromotion. The observed stress distribution was better in the 30° and 45° models than in the 0° and 15° models.     

Zinc silicate phosphor: Insights of X-ray induced and temperature enabled luminescence

The present investigation deals with the effect of calcination temperature on the structural and thermoluminescent (TL) properties of Zn₂SiO₄ materials. For this study, Zn₂SiO₄ was prepared via a simple hydrothermal route and calcinated at temperatures from 700°C to 1100°C in an air atmosphere. TL data of all Zn₂SiO₄ samples showed two peaks at around 240°C and 330°C due to the formation of the luminescence centre during X-ray irradiation. More interestingly, the Zn₂SiO₄ sample calcinated at 900°C exhibited a shift in the TL peak (282°C and 354°C) with an optimal TL intensity attributed to its good crystallinity with a well-defined hexagonal plate-like morphology. X-ray-irradiated Zn₂SiO₄ samples calcinated at 900°C exhibited a high-temperature TL glow curve peak, suggesting that the present material could be used for high-temperature dosimetry applications.     

Effects of circadian rhythms of fluctuating temperature on growth and biochemical composition of <Emphasis Type="Italic">Ulva pertusa</Emphasis>

The marcoalga Ulva pertusa was cultured under (20 ± 2)°C, (20 ± 4)°C, (20 ± 6)°C, (20 ± 8)°C and (20 ± 10)°C circadian rhythms of fluctuating temperature conditions, and constant temperature of 20°C was used as the control. The growth rate of macroalga at (20 ± 2)°C, (20 ± 4)°C and (20 ± 6)°C were significantly higher than that at constant temperature of 20°C, while growth rate at (20 ± 8)°C and (20 ± 10)°C were significantly lower than that at constant temperature of 20°C. The growth rate of macroalga was a quadratic function of the thermal amplitude. Such a growth model can be described by G = β ₀ + β ₁(TA) + β ₂(TA)², where G represents the relative growth rate, TA is thermal amplitude in degree Celsius, β ₀ is the intercept on the G axis, and β ₁ and β ₂ are the regression coefficients. The optimal thermal amplitude for the growth of thallus at mean temperature of 20°C was estimated to be ± 3.69°C. Analysis of biochemical composition at the final stages of thaulls growth revealed that diel fluctuating temperature caused various influences (P < 0.05). The content of chlorophyll, protein and total solute carbohydrate at (20 ± 2)°C and (20 ± 4)°C were slightly higher than those at constant temperature of 20°C, however no statistically significant differences were found among them (P > 0.05). While osmolytes (total solute carbohydrate and free proline) at (20 ± 10)°C were significantly higher than that at 20°C (P < 0.05). Therefore, more chlorophyll and carbohydrate production might account for the enhancement in the growth of macroalga at the diel fluctuating temperatures in the present study. Handling editor: S. M. Thomaz     

Spectroelectrochemistry of ferrioxamine B,ferrichrome, and ferrichrome A

Thin-layer spectroelectrochemical techniques were used to determine the entropy change for the reduction of the three siderophores ferrioxamine B, ferrichrome, and ferrichrome A. The entropy changes were found to be large and negative. The _ΔS° values obtained are: ferrioxamine B. pH 10.2, _ΔS° = ?33.3 ± 0.4 eu; pH 9.0, _ΔS° = ?26.9 ± 0.9 eu; pH 8.0, _ΔS° = ?23.3 ± 1.2 eu; ferrichrome, pH 10.0, ΔS° = ?42.6 ± 0.5 eu; pH 9.1, ΔS° = ?35.8 ± 0.4 eu; pH 7.3, ΔS° = ?74.5 ± 3.4 eu; ferrichrome A, pH 10.1, _ΔS° = ?35.6 ± 0.9 eu; pH 9.1, _ΔS° = ?34.3 ± 0.9 eu; pH 7.9, _ΔS° = ?31.7 ± 0.9 eu. These values are adjusted to the scale on which S°_H + = 0. The large decreases in entropy upon reduction are attributed to an increase in the solvent ordering around the ferrous complex. Upon reduction, the rigid structure of the ferric chelate is loosened and previously sequestered amide groups are made available for solvent interactions. This increased interaction with solvent causes an increase in the order of the water around the molecule and this is responsible for the observed entropy changes. Variations in ΔS° values and the pH dependencies of these values are attributed to structural peculiarities of the individual siderophores.     

Low Root Temperature Retardation of the Mineral Nitrogen Induced Decline in N2Fixation by a Northern Ecotype of White Clover

Nodulated white clover plants (Trifolium repensL.) of a Norwegian ecotype from Pasvik (70°N) were grown in flowing solution culture. Root temperature was 17°C until 51d after sowing, when it was lowered decrementally over 5d to 7°C in four of the eight plant culture units. After a further 24h, mineral N was supplied automatically at 20μMNH₄NO₃in three culture units at each root temperature (7 and 17°C) over 17d. The remaining two units provided control plants solely dependent on N₂fixation at 7 and 17°C.The supply of NH₄NO₃greatly reduced the nodule biomass per plant at 17°C over 17d compared with control plants, but had little effect at 7°C. The nodule decline at 17°C accompanied an acute and progressive decrease in specific rate of N₂fixation, from 9mmolN d^-1g^-1nodule d.wt on day 0 to zero by day 10. Whilst initial rates of N₂fixation were lower at 7°C, the mineral N-induced decrease in fixation rates was also less severe than at 17°C and specific fixation rates recovered after reaching a minimum on day 11. N₂fixation accounted for 36% of the total uptake of N by +min.N plants during the treatment period at 7°C as opposed to only 13% at 17°C. The total N₂fixed at 7°C was 86% of that fixed at 17°C, although the specific growth rate (d.wt) at 7°C was only 55% of that at 17°C. Addition of NH₄NO₃at 7°C had little effect on the gross amount of N₂fixed subsequently. In contrast, total N₂fixation by +min.N plants at 17°C was only 24% of that fixed by the corresponding controls. The possible mechanisms by which mineral N affects N₂fixation are discussed.     

Brain temperature regulation of panting and non-panting pigeons exposed to extreme thermal conditions

• 1.1. Brain (hypothalamic), skin and body temperatures were measured in hand-reared acclimated (Acc, n = 5) and non-acclimated (NAcc, n =7) rock pigeons (Columba livia, mean body mass 237 g) exposed to increasing ambient temperatures (T_a) (30–60°C) and low humidities.
• 2.2. In non-panting Acc birds, brain temperature gradually increased from 40.1 ± 0.4°C at 30°C to 41.2 ± 0.4°C at 60°C T_a. A mean body temperature (T_b) of 41.2 ± 0.2°C was measured at T_a up to 50°C; an increase of 1.1°C was observed at 60°C (T_b 42.2 ±0.6°C).
• 3.3. In Acc panting birds exposed for 2 hr to 60°C, T_hy was 41.9 ± 0.8°C and T_s was somewhat (but insignificantly) higher, i.e., 42.2 ± 0.7°C. It looks as if both values were increased as a result of a slight hyperthermia that developed (T_b = 43.5 ± 0.9°C).
• 4.4. The significance of the present results for evaluating neuronal thermoresponsiveness of birds' hypothalamus is discussed.

     

Effect of temperature on ion content, ion fluxes and energy metabolism in Chara corallina

Abstract Effects of temperature on the ionic relations and energy metabolism of Chara corallina were investigated. Measurements were made of the ionic content, tracer ion fluxes, and photosynthetic and dark CO₂ fixation in isolated cells, and of O₂ exchange in photosynthesis and respiration in isolated shoot apices. The total intracellular concentration of K⁺, Na⁺ and Cl^? was the same in cells held for 5 days in non-growing medium at 15°C (the growth temperature) as in those held at 25°C or 5°C. The tracer influx in the light of all ions tested (Rb⁺, Na⁺, CH₃NH₃⁺, Cl^? and H₂PO₄^?) was lower at 5°C than at 15°C in experiments in which cells were subjected to 5°C for less than 24 h in toto. The influx at 25°C was greater than that at 15°C for H₂PO^?₄, there was no difference between the two temperatures for Na⁺, while the influx at 25°C was less than that at 15°C for Cl^?, Rb⁺ and CH₃NH₃⁺ For Cl^? and H₂PO^?₄ similar results were found in later experiments with cells grown at 20—23°C. Photosynthetic CO₂ fixation and O₂ evolution, and respiratory O₂ uptake, are greater at 25°C, and lower at 5°C, than they are at the growth temperature of 15°C. In longer-term pretreatments at the different temperatures, tracer Cl^? influx at 15°C and particularly at 25°C were lower than in short-term experiments, while the influx at 5°C was higher. It was concluded from these experiments, and from previous data on H⁺ free energy differences across the plasmalemma, that (1) the maintenance of internal ion concentrations involves a close balancing of influx and efflux of K⁺, Na⁺ and Cl^? at all experimental temperatures; (2) the regulation of the tracer fluxes of the ions is kinetic rather than thermodynamic and (3) that the tracer fluxes at low temperatures are not restricted by the rate at which respiration or photosynthesis can supply energy to them.     

Constant and fluctuating temperature acclimations have similar effects on phenotypic plasticity in springtails

Much interest exists in the extent to which constant versus fluctuating temperatures affect thermal performance traits and their phenotypic plasticity. Theory suggests that effects should vary with temperature, being especially pronounced at more extreme low (because of thermal respite) and high (because of Jensen's inequality) temperatures. Here we tested this idea by examining the effects of constant temperatures (10 to 30 °C in 5 °C increments) and fluctuating temperatures (means equal to the constant temperatures, but with fluctuations of ±5 °C) temperatures on the adult (F2) phenotypic plasticity of three thermal performance traits – critical thermal minimum (CT_min), critical thermal maximum (CT_max), and upper lethal temperature (ULT₅₀) in ten species of springtails (Collembola) from three families (Isotomidae 7 spp.; Entomobryidae 2 spp.; Onychiuridae 1 sp.). The lowest mean CT_min value recorded here was -3.56 ± 1.0 °C for Paristoma notabilis and the highest mean CT_max was 43.1 ± 0.8 °C for Hemisotoma thermophila. The Acclimation Response Ratio for CT_min was on average 0.12 °C/°C (range: 0.04 to 0.21 °C/°C), but was much lower for CT_max (mean: 0.017 °C/°C, range: -0.015 to 0.047 °C/°C) and lower also for ULT₅₀ (mean: 0.05 °C/°C, range: -0.007 to 0.14 °C/°C). Fluctuating versus constant temperatures typically had little effect on adult phenotypic plasticity, with effect sizes either no different from zero, or inconsistent in the direction of difference. Previous work assessing adult phenotypic plasticity of these thermal performance traits across a range of constant temperatures can thus be applied to a broader range of circumstances in springtails.     

Conformational variability of Gly-Gly segments in peptides: A comparison of the crystal structures of an acyclic pentapeptide and an octapeptide

The crystal structure of an acyclic pentapeptide, Boc-Gly-Gly-Leu-Aib-Val-OMe, reveals an extended conformation for the Gly-Gly segment, in contrast to the helical conformation determined earlier in the octapeptide Boc-Leu-Aib-Val-Gly-Gly-Leu-Aib-Val-OMe [I. L. Karle, A. Banerjee, S. Bhattacharjya, and P. Balaram [1996] Biopolymers, Vol. 38, pp. 515–526). The pentapeptide crystallizes in space group P2₁ with one molecule in the asymmetric unit. The cell parameters are: a = 10.979(2) Å, b = 9.625(2) Å, c = 14.141(2) Å, and β = 96.93(1)°, R = 6.7% for 2501 reflections (I > 3σ(I)). The Gly-Gly segment is extended (ϕ₁ = −92°, ψ₁ = −133°, ϕ₂ = 140°, ψ₂ = 170°), while the Leu-Aib segment adopts a type II β-turn conformation (ϕ₃ = −61°, ψ₃ = 130°, ϕ₄ = 71°, ψ₄ = 6°). The observed conformation for the pentapeptide permits rationalization of a structural transition observed for the octapeptide in solution. An analysis of Gly-Gly segments in peptide crystal structures shows a preference for either β-turn or extended conformations. © 1997 John Wiley & Sons, Inc.     

Ground cavity nest temperatures and their relevance to Blue Swallow Hirundo atrocaerulea conservation

Blue Swallows Hirundo atrocaerulea are Critically Endangered within South Africa. They nest in natural underground holes in mist-belt grasslands. Temperature dataloggers were used to record ground cavity nest (T_n) and ambient temperature (T_a) for one artificial and 11 natural Blue Swallow nests. Mean ground cavity T_n was significantly different to mean T_a. T_n ranged from 17.0 ± 0.1 °C to 28.5 ± 0.3 °C and varied less than T_a (14.0 ± 0.2 to 47.7 ± 0.4 °C). Mean ground cavity T_n averaged 3.3 ± 0.9 °C warmer than mean T_a for 58% of nests, and mean T_a averaged 2.6 ± 0.5 °C warmer than mean ground cavity T_n for 42% of nests. There was no significant difference in mean ground cavity T_n for the aardvark-excavated holes (22.7 ± 1.6 °C) and sinkholes (21.5 ± 1.2 °C). Blue Swallows also nest in man-made holes, potentially a way to increase nesting sites. Mean aardvark-excavated T_n (19.2 ± 0.1 °C) was significantly warmer than mean artificial cavity T_n (18.5 ± 0.2 °C). Further investigation of breeding success of Blue Swallows in relation to T_n, incubation strategies and predation risk needs to be addressed in future studies for a better understanding of their reproductive ecology.     

Temperature Dependency of Circadian Period in a Single Cell (Acetabularia)

The circadian rhythm in the oxygen production of 30 individual Acetabularia cells has been studied at different temperatures. The temperature induced period variation was continuously evaluated over the whole data record of each individual cell with an advanced spectral analysis technique. The observed circadian periods of O₂ production displayed a well established region of temperature compensation between 25 °C and 30 °C with a Q₁₀, value of 0.9, whereas between 15°C and 22°C a positive temperature coefficient was measured (Q₁₀ at 22 °C 0.9, Q₁₀ at 20°C 0.8, Q₁₀at 17°C 0.7).     

Design of Peptides Using α,β-Dehydro-residues: Synthesis,Crystal Structure and Molecular Conformation of N-Boc-L-Val-ΔPhe–ΔPhe-L-Ala-OCH3

To obtain general rules of peptide design using α,β-dehydro-residues, a sequence with two consecutive ΔPhe-residues, Boc-L -Val-ΔPhe–ΔPhe- L -Ala-OCH₃, was synthesized by azlactone method in solution phase. The peptide was crystallized from its solution in an acetone/water mixture (70:30) in space group P6₁ with a=b=14.912(3) Å, c= 25.548(5) Å, V=4912.0(6) ų. The structure was determined by direct methods and refined by a full matrix least-squares procedure to an R value of 0.079 for 2891 observed [I?3σ(I)] reflections. The backbone torsion angles ?₁=?54(1)°, ψ₁= 129(1)°, ω₁=?177(1)°, ?₂ =57(1)°, ψ₂=15(1)°, ω₂ =?170(1)°, ?₃=80(1)°, ψ₃ =7(2)°, ω₃=?177(1)°, ?₄ =?108(1)° and ψ^T₄=?34 (1)° suggest that the peptide adopts a folded conformation with two overlapping β-turns of types II and III′. These turns are stabilized by two intramolecular hydrogen bonds between the CO of the Boc group and the NH of ΔPhe³ and the CO of Val¹ and the NH of Ala⁴. The torsion angles of ΔPhe² and ΔPhe³ side chains are similar and indicate that the two ΔPhe residues are essentially planar. The folded molecules form head-to- tail intermolecular hydrogen bonds giving rise to continuous helical columns which run parallel to the c-axis. This structure established the formation of two β-turns of types II and III′ respectively for sequences containing two consecutive ΔPhe residues at (i+2) and (i+3) positions with a branched β-carbon residue at one end of the tetrapeptide.     

Changes in exercise and post-exercise core temperature under different clothing conditions

 This study evaluates the effect of different levels of insulation on esophageal (T _es) and rectal (T _re) temperature responses during and following moderate exercise. Seven subjects completed three 18-min bouts of treadmill exercise (75% VO_2max, 22°C ambient temperature) followed by 30 min of recovery wearing either: (1) jogging shoes, T-shirt and shorts (athletic clothing); (2) single-knit commercial coveralls worn over the athletic clothing (coveralls); or (3) a Canadian Armed Forces nuclear, bacteriological and chemical warfare protective overgarment with hood, worn over the athletic clothing (NBCW overgarment). T _es was similar at the start of exercise for each condition and baseline T _re was ∼0.4°C higher than T _es. The hourly equivalent rate of increase in T _es during the final 5 min of exercise was 1.8°C, 3.0°C and 4.2°C for athletic clothing, coveralls and NBCW overgarment respectively (P<0.05). End-exercise T _es was significantly different between conditions [37.7°C (SEM 0.1°C), 38.2°C (SEM 0.2°C and 38.5°C (SEM 0.2°C) for athletic clothing, coveralls and NBCW overgarment respectively)] (P<0.05). No comparable difference in the rate of temperature increase for T _re was demonstrated, except that end-exercise T _re for the NBCW overgarment condition was significantly greater (0.5°C) than that for the athletic clothing condition. There was a drop in T _es during the initial minutes of recovery to sustained plateaus which were significantly (P<0.05) elevated above pre-exercise resting values by 0.6°C, 0.8°C and 1.0°C, for athletic clothing, coveralls, and NBCW overgarment, respectively. Post-exercise T _re decreased very gradually from end-exercise values during the 30-min recovery. Only the NBCW overgarment condition T _re was significantly elevated (0.3°C) above the athletic clothing condition (P<0.05). In conclusion, T _es is far more sensitive in reflecting the heat stress of different levels of insulation during exercise and post-exercise than T _re. Physiological mechanisms are discussed as possible explanations for the differences in response. Received: 30 June 1998 / Accepted: 19 February 1999     

Observation of a sterically unfavorable side-chain conformation in a leucyl residue: Crystal and molecular structure of L-leucyl–L-leucine · DMSO solvate

The crystal structure of a dipeptide L -leucyl–L -leucine (C₁₂H₂₄N₂O₃) has been determined. The crystals are monoclinic, space group P2₁, with a = 5.434(4) Å, b = 15.712(7) Å, c = 11.275(2) Å, β = 100.41(1)°, and Z = 2. The crystals contain one molecule of dimethyl sulfoxide (DMSO) as solvent of crystallization for each dipeptide molecule. The structure has been solved by direct methods and refined to a final R index of 0.059 for 920 reflections (sinθ/λ ? 0.60 Å^?1) with I ? 2σ (I). The trans peptide unit shows substantial degree of non-planarity (Δω = 14°). The peptide backbone adopts an extended conformation with torsion angles of ψ₁ = 138(1)°, ω₁ = 166(1)°, ?₂ = ? 149.3(7)°, ψ₂₁ = 164.2(7)°, and ψ₂₂ = ? 15(1)°. For the first leucyl residue, the side-chain conformation is specified by the torsion angles ¹χ₁ = 176.7(7)°, ¹χ₂₁ = 62(1)°, ¹χ₂₂ = ? 177.4(8)°; the second leucyl residue adopts a Sterically unfavorable conformation with ²χ₁ = 61(1)°, ²χ₂₁ = 97(1)°, and ²χ₂₂ = ?151(1)°. The packing involves head-to-tail interaction of peptide molecules and segregation of polar and nonpolar regions. The DMSO molecule is strongly hydrogen bonded to the terminal NH group. © 1994 John Wiley & Sons, Inc.     

Photosynthetic capacity and temperature responses of photosynthesis of rubber trees (Hevea brasiliensis Müll. Arg.) acclimate to changes in ambient temperatures

The aim of this study was to assess the temperature response of photosynthesis in rubber trees (Hevea brasiliensis Müll. Arg.) to provide data for process-based growth modeling, and to test whether photosynthetic capacity and temperature response of photosynthesis acclimates to changes in ambient temperature. Net CO₂ assimilation rate (A) was measured in rubber saplings grown in a nursery or in growth chambers at 18 and 28°C. The temperature response of A was measured from 9 to 45°C and the data were fitted to an empirical model. Photosynthetic capacity (maximal carboxylation rate, V _cmax, and maximal light driven electron flux, J _max) of plants acclimated to 18 and 28°C were estimated by fitting a biochemical photosynthesis model to the CO₂ response curves (A–C _i curves) at six temperatures: 15, 22, 28, 32, 36 and 40°C. The optimal temperature for A (T _opt) was much lower in plants grown at 18°C compared to 28°C and nursery. Net CO₂ assimilation rate at optimal temperature (A _opt), V _cmax and J _max at a reference temperature of 25°C (V _cmax25 and J _max25) as well as activation energy of V _cmax and J _max (E _aV and E _aJ) decreased in individuals acclimated to 18°C. The optimal temperature for V _cmax and J _max could not be clearly defined from our response curves, as they always were above 36°C and not far from 40°C. The ratio J _max25/V _cmax25 was larger in plants acclimated to 18°C. Less nitrogen was present and photosynthetic nitrogen use efficiency (V _cmax25/N _a) was smaller in leaves acclimated to 18°C. These results indicate that rubber saplings acclimated their photosynthetic characteristics in response to growth temperature, and that higher temperatures resulted in an enhanced photosynthetic capacity in the leaves, as well as larger activation energy for photosynthesis.     

Effects of root temperature on leaf gas exchange and xylem sap abscisic acid concentrations in six Cucurbitaceae species

Roots of six Cucurbitaceae species were exposed to low (14 °C), middle (24 °C), and high (34 °C) temperatures while aerial parts of plants were maintained at ambient temperatures between 23 and 33 °C. The highest dry mass (DM), photon-saturated rate of net photosynthesis (P _Nsat), and stomatal conductance (g _s) were found at 14 °C in figleaf gourd and turban squash plants, at 24 °C in cucumber and melon plants, while bitter melon and wax gourd plants had lower DM, P _Nsat, and g _s at 14 °C than at 24 or 34 °C. Sub-or supra-optimum root temperatures did not induce photoinhibition but induced slight changes in the quantum efficiency of photosystem 2, PS2 (Φ_PS2) and photochemical quenching (q_p). Meanwhile, xylem sap abscisic acid (ABA) concentration followed a contrasting change pattern to that of g _s. Thus the change in P _Nsat was mainly due to the change in g _s and roots played an important role in the regulation of stomatal behaviour by delivering increased amount of ABA to shoots at sub-or supra-optimum root temperatures.